one way is to include a rule that rewrites a URL to itself. Something like this;

# Rewrite any URL to "itself". ($0 matches all of the incoming
# URL path.) This rule is decorated with the L modifier to indicate
# :Last rule:, which means rule processing will not iterate further
# after this rule fires. No endless loops. Also, it gets the U modifer
# which says to set the HTTP_X_REWRITE_URL variable with
# the original. This rule should always appear LAST in the
# IIRf.ini file, so as not to pre-empt any other rules.
RewriteRule ^/.* $0 [U,L]